Imaging systems include scanner systems, staring systems (also known as step-staring systems), and time-delay integration (TDI) systems. Scanning systems include push broom scanners (also known as an along-track scanners), and whisk broom scanners (also known as across-track scanners). Scanning arrays are constructed from linear arrays (or very narrow 2-D arrays), that are rastered across a desired field of view using a rotating or oscillating mirror to construct a 2-D image over time. A TDI imager operates in similar fashion to a scanning array except that it images perpendicularly to the motion of the camera. A staring array is analogous to the film in a typical camera, in that it directly captures a 2-D image projected by a lens at an image plane. A scanning array is analogous to piecing together a 2D image with photos taken through a narrow slit. A TDI imager is analogous to looking through a vertical slit out the side window of a moving car, and building a long, continuous image as the car passes the landscape.
There is a demand for satellite-based hyperspectral imaging data collected over a wide area of the earth at fine spatial resolution. Fourier Transform Spectroscopy (FTS) instruments provide relatively high quality hyperspectral data. Conventional FTS system are operated as a step-stare systems, which require relatively fast focal plane array (FPA) frame rates to collect an interferogram while staring. This tends to the maximum size of the FPA, and thus requires fast step-staring to achieve a wide swath width. The resulting short stare time negatively impacts signal-to-noise ratio (SNR), and increases instrument complexity. As a result, FTS is normally not used for wide swath widths. Instead, dispersive systems are used, which provide inferior data quality, and tend to have higher cooling needs.
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